Stimulation of cartilage formation using reduced pressure treatment

ABSTRACT

A method of inducing new cartilage growth from periosteum in a mammal is provided. The method includes positioning a foam manifold in contact with the periosteum and positioning a drape over the foam manifold and the periosteum to create a sealed space between the drape and the periosteum. A reduced pressure is applied to the sealed space.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/491,445, filed Jun. 25, 2009, which claims the benefit of U.S.Provisional Application No. 61/076,028, filed Jun. 26, 2008, all ofwhich are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to tissue treatment systems andin particular to methods for stimulating cartilage formation.

2. Description of Related Art

Clinical studies and practice have shown that providing a reducedpressure in proximity to a tissue site augments and accelerates thegrowth of new tissue at the tissue site. The applications of thisphenomenon are numerous, but application of reduced pressure has beenparticularly successful in treating wounds. This treatment (frequentlyreferred to in the medical community as “negative pressure woundtherapy,” “reduced pressure therapy,” or “vacuum therapy”) provides anumber of benefits, including faster healing and increased formulationof granulation tissue. Typically, reduced pressure is applied to tissuethrough a porous pad or other manifolding device. Unless otherwiseindicated, as used herein, “or” does not require mutual exclusivity. Theporous pad, often an open-cell foam, contains cells or pores that arecapable of distributing reduced pressure to the tissue and channelingfluids that are drawn from the tissue. The porous pad is generally sizedto fit the existing wound, placed in contact with the wound, and thenperiodically replaced with smaller pieces of foam as the wound begins toheal and becomes smaller. The porous pad often is incorporated into adressing having other components that facilitate treatment. Whilereduced pressure therapy has been used to treat soft tissue injuries, ithas not been used to promote, for example, cartilage regeneration.

Damage to cartilage through age, injury, wear and metabolic disorders,such as osteoarthritis, affect millions of people throughout the world.Indeed, it is currently believed that 85% of all Americans will developdegenerative joint disease as a result of normal activities that damagecartilage. The gradual degeneration and destruction of articularcartilage may be due to trauma, structural deformation of the joints andbeing overweight. The process thins the cartilage, in part throughprogrammed cell death, or apoptosis. The clinical manifestations ofcartilage damage or wear are often painful and debilitating, includingswelling of the joint, crepitation, and decrease in functional mobility.As the condition worsens, pain may even limit minimum physical effortsand persist at rest making it difficult to sleep. If the conditionpersists without correction and/or therapy, the joint can be totallydestroyed, leading the patient to major replacement surgery with a totalprosthesis, or to disability. The complications of cartilage injury aremultifold. For example, injured cartilage tends to cause additionaldamage to articulations and the articular surfaces. Damage to articularsurfaces is linked to bone spur development, which further limits jointmovement.

Moreover, cartilage is the main structural support of various parts ofthe body, such as ears and the nose. As such, a lack of cartilage frominjury may also result in a cosmetic defect. Thus, in sum, damaged anddegraded cartilage results in a reduced quality of life.

The body, however, cannot completely repair the cartilage. Cartilage isprimarily composed of collagen fibers, proteoglycans and elastin fibersthat form an extracellular matrix. The matrix is formed by specializedcells called chondrocytes. Chondrocytes are one of the few cell typesthat can survive with a minimal blood supply. However, when cartilage isdamaged, the lack of an adequate blood supply to the chondrocytesresults in an inability to regenerate new chondrocytes, a process thatrequires an increased amount of nutrients and access through the bloodstream to other cells and proteins. Full thickness articular cartilagedamage or osteochondral lesions may allow for normal inflammatoryresponse, but then result in repair with functionally inferiorfibrocartilage formation.

Current techniques to inhibit or delay degeneration of joint cartilageinclude use of anti-inflammatory agents, chondrogenic stimulatingfactors, antirheumatics, systemics, viscoprotection and injection ofdepot steroids. Other methods include implantation of chondrocytes orsynthetic matrices. One method of treatment for cartilage damage issurgical intervention, with reattachment and reconstruction of thedamaged tissue. None of the above methods are totally satisfactory, andthose methods rarely restore full function or return the tissue to itsnative normal state. In addition, none, of those methods are proven toregenerate cartilage in situ and in vivo.

Further, there is no proven way to promote healing of dense connectivetissue structures such as ligaments and tendons. Ligament and tendoninjuries are commonplace and difficult to heal. Indeed, it is notuncommon to repair complete ruptures or tears of a ligament or tendon byimmediate surgery to remove the damaged tissue and replace it with agraft. Post surgery, a graft recipient has to experience the long taskof rehabilitation and healing. It is often difficult to repair ligamentsand tendons by current methods. Thus, when repair is an option, thejoints and muscles attached to the ligament or tendon are oftenimmobilized to enable the tissue to heal.

As such, there is currently an acute need for a safe, simple, rapid,inexpensive and efficient system and method for regenerating connectivetissues in areas where the connective tissue is missing, damaged, orworn.

SUMMARY

The problems presented by existing cartilage repair treatment regimensare solved by the systems and methods presented by the illustrativeembodiments described herein. In one embodiment, a method of inducingnew cartilage growth from periosteum includes positioning a foammanifold in contact with the periosteum. The method further includespositioning a drape over the foam manifold and the periosteum to createa sealed space between the drape and the periosteum. A reduced pressureis applied to the sealed space.

In another embodiment, a method of stimulating cartilage formation at atissue site having periosteum is provided. The method includes applyinga foam manifold to the periosteum and applying reduced pressure to thefoam manifold and the tissue site for a time sufficient to cause newcartilage formation at the tissue site.

In still another embodiment, a system for stimulating cartilageformation at a tissue site includes a foam manifold positioned incontact with periosteum at the tissue site. A drape is positioned overthe foam manifold and the tissue site to create a sealed space betweenthe drape and the tissue site. A reduced pressure source is in fluidcommunication with the sealed space.

Other objects, features, and advantages of the illustrative embodimentswill become apparent with reference to the drawings and detaileddescription that follow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustrative embodiment of a reduced-pressure therapysystem for treating tissue;

FIG. 2 is a flow chart illustrating a method of administering a reducedpressure therapy to a tissue site requiring cartilage regenerationaccording to an illustrative embodiment;

FIG. 3 illustrates use of a mold to facilitate administration of reducedpressure therapy to induce connective tissue regeneration according toan illustrative embodiment; and

FIGS. 4A-4C illustrate histological sections demonstrating the resultsof reduced pressure therapy for cartilage regeneration according to anillustrative embodiment.

DETAILED DESCRIPTION

In the following detailed description of the illustrative embodiments,reference is made to the accompanying drawings that form a part hereof.These embodiments are described in sufficient detail to enable thoseskilled in the art to practice the invention, and it is understood thatother embodiments may be utilized and that logical structural,mechanical, electrical, and chemical changes may be made withoutdeparting from the spirit or scope of the invention. To avoid detail notnecessary to enable those skilled in the art to practice the embodimentsdescribed herein, the description may omit certain information known tothose skilled in the art. The following detailed description is,therefore, not to be taken in a limiting sense, and the scope of theillustrative embodiments are defined only by the appended claims.

The term “reduced pressure” as used herein generally refers to apressure less than the ambient pressure at a tissue site that is beingsubjected to treatment. In most cases, this reduced pressure will beless than the atmospheric pressure at which the patient is located.Alternatively, the reduced pressure may be less than a hydrostaticpressure associated with tissue at the tissue site Although the terms“vacuum” and “negative pressure” may be used to describe the pressureapplied to the tissue site, the actual pressure reduction applied to thetissue site may be significantly less than the pressure reductionnormally associated with a complete vacuum. Reduced pressure mayinitially generate fluid flow in the area of the tissue site. As thehydrostatic pressure around the tissue site approaches the desiredreduced pressure, the flow may subside, and the reduced pressure is thenmaintained. Unless otherwise indicated, values of pressure stated hereinare gauge pressures. Similarly, references to increases in reducedpressure typically refer to a decrease in absolute pressure, whiledecreases in reduced pressure typically refer to an increase in absolutepressure.

The term “tissue site” as used herein refers to the location of a woundor defect on or within any tissue, including but not limited to, bonetissue, adipose tissue, muscle tissue, neural tissue, dermal tissue,vascular tissue, connective tissue, cartilage, tendons, or ligaments.The term “tissue site” may further refer to areas of any tissue that arenot necessarily wounded or defective, but are instead areas in which itis desired to add or promote the growth of additional tissue. Forexample, reduced pressure tissue treatment may be used in certain tissueareas to grow additional tissue that may be harvested and transplantedto another tissue location.

Referring to FIG. 1, an illustrative embodiment of a system 100 forapplying reduced-pressure therapy to a tissue site 102 is shown. Theillustrative embodiments of the system 100 apply reduced-pressuretherapy to a wound 106 at the tissue site 102 which includes, forexample, cartilage that needs to be repaired by regeneration. It shouldbe understood that the tissue site 102 may be the bodily tissue of anyhuman, animal, or other organism, including bone tissue, adipose tissue,muscle tissue, dermal tissue, vascular tissue, connective tissue,cartilage, tendons, ligaments, or any other tissue. Treatment of tissuesite 102 may include removal of fluids, e.g., ascites or exudate,delivery of fluids, e.g., saline or materials such as growth factors,and delivery of reduced pressure, for facilitating the growth ofcartilage. The cartilage wound 106 on the tissue site 102 may be due avariety of causes, including trauma, surgery, wear, arthritis, cancer,etc., or may be congenital.

The system 100 comprises a reduced pressure dressing 110, which includesa manifold 111 adapted to distribute the reduced pressure to the tissuesite 102 and a scaffold 112 adapted for placement adjacent the wound106, and a drape 114 at least partially covering the reduced pressuredressing 110 to provide a seal covering the wound 106 at the tissue site102. A chondrocyte or chondrocyte precursor can be placed directly onthe tissue site 102 or be contained within a scaffold 112 that isapplied to the tissue site 102. The system 100 further comprises acanister 115 with a filter (not shown) and a reduced pressure source116, wherein the canister 115 is in fluid communication with the reducedpressure dressing 110 via a conduit 118 and is also in fluidcommunication with the reduced pressure source 116 via a conduit 119.The reduced pressure source 116 is adapted to supply reduced pressure tothe manifold 111 and the scaffold 112 which distribute the reducedpressure to the tissue site 102 when in operation. The conduit 118 mayfluidly communicate with the reduced pressure dressing 110 through atubing adapter 120 to provide the reduced pressure through the drape 114to the manifold 111.

In yet another embodiment, the reduced pressure dressing 110 may beconstructed from multiple layers or materials in addition to or in lieuof the manifold 111, the scaffold 112, and the drape 114. Some of theselayers may be bioabsorbable while others are not. For instance, themanifold 111 may include a bioabsorbable material adjacent to abio-inert material or a bioabsorbable material that degrades more slowly(as the terms are defined below), such that the reduced pressuredressing 110 may be removed and replaced without removal of anyabsorbable scaffold 112, that supports tissue growth, from the wound106.

The canister 115 may be a fluid reservoir, or collection member, tofilter and hold exudates and other fluids removed from the tissue site102. The canister 115 may include other devices (not shown) includingthe following non-limiting examples: a pressure-feedback device, avolume detection system, a blood detection system, an infectiondetection system, a flow monitoring system, and a temperature monitoringsystem. Some of these devices may be formed integral with thereduce-pressure source 116. For example, a reduced-pressure port on thereduced-pressure source 116 may include a filter member that includesone or more filters, e.g., an odor filter.

The reduced-pressure source 116 may be any device for supplying areduced pressure, such as a vacuum pump, wall suction, or other source.While the amount and nature of reduced pressure applied to a tissue sitewill typically vary according to the application, the reduced pressurewill typically be between −5 mm Hg and −500 mm Hg and more typicallybetween −100 mm Hg and −300 mm Hg. The particular protocol used inreduced pressure treatment depends upon the location of the tissue site102, the reduced pressure dressing 110, or pharmacological agents beingutilized. Additionally, reduced pressure may be a substantiallycontinuous or cyclical application such that it oscillates the pressureover time. The reduced pressure source 116 may include sensors,processing units, alarm indicators, memory, databases, software, displayunits, and user interfaces that further facilitate the application ofreduced pressure treatment to the tissue site 102. In one example, asensor or switch (not shown) may be disposed at or near the reducedpressure source 116 to determine a source pressure generated by thereduced pressure source 116. The sensor may communicate with aprocessing unit that monitors and controls the reduced pressure but isdelivered by the reduced pressure source 116.

The cartilage may be any type of cartilage. For example, hyalinecartilage is the most common type of cartilage in the body andcharacteristically contains collagen type II fibers in its extracellularmatrix. Hyaline cartilage is found in articular joints, costal cartilage(ribs), nose, larynx, and growth plate. Another type of cartilage iselastic cartilage found in ear, trachea and epiglottis. The third typeof cartilaginous tissue, fibrocartilage, is present in the pubicsymphysis, intervertebral disc, parts of the articular joints, menisciand in sites connecting tendons or ligaments to bones. There also existvarious combinations or intermediates of these types of cartilage, suchas the epiphyseal cartilage in the growth or cartilage plate.

The manifold 111 of the reduced pressure dressing 110 is adapted tocontact the scaffold 112 or portions of the tissue site 102. Themanifold 111 may be partially or fully in contact with the tissue site102 being treated by the reduced pressure dressing 110. When the tissuesite 102 is a wound, the manifold 111 may partially or fully fill thewound. The manifold 111 may be any size, shape, or thickness dependingon a variety of factors, such as a type of treatment being implementedor the nature and size of the tissue site 102. For example, the size andshape of the manifold 111 may be customized by a user to cover aparticular portion of the scaffold 112 and/or the tissue site 102. Themanifold 111 may have, for example, a square shape, or may be shaped asa circle, polygon, an irregular shape, or any other shape. In oneillustrative embodiment, the manifold 111 is a foam material thatdistributes reduced pressure to the scaffold 112 and the tissue site 102when the manifold 111 is in contact with, or near, the scaffold 112.Foam material may be either hydrophobic or hydrophilic. In onenon-limiting example, the manifold 111 is an open-cell, articulatedpolyurethane foam such as GranuFoam®dressing available from KineticConcepts, Inc. of San Antonio, Tex.

In some embodiments, the manifold 111 is made from a hydrophilicmaterial, where the manifold 111 functions to wick fluid away from thetissue site 102, while continuing to provide reduced pressure to thescaffold 112 and the tissue site 102 as a manifold. Without being boundby any particular mechanism, the wicking properties of the manifold 111can draw fluid away from the scaffold 112 and the tissue site 102 bycapillary flow or other wicking mechanisms. An example of hydrophilicfoam is a polyvinyl alcohol, open-cell foam such as V.A.C. WhiteFoam®dressing available from Kinetic Concepts, Inc. of San Antonio, Tex.Other hydrophilic foams may include those made from polyether.Additional foams that may exhibit hydrophilic characteristics includehydrophobic foams that have been treated or were coated to providehydrophilicity.

In another embodiment, the manifold 111 is constructed from abioabsorbable material, natural or synthetic, that does not have to beremoved from the tissue site 102 following use of the reduced pressuredressing 110. Bioabsorbable material is material that is capable ofbeing absorbed in the body or removed from the body by excretion ormetabolic functions; prior to absorption, the bioabsorbable material maybe chemically, enzymatically, or otherwise degraded in vivo into simplerchemical species. Suitable bioresorbable materials may include, withoutlimitation, a polymeric blend of polylactic acid (PLA) and polyglycolicacid (PGA). The polymeric blend may also include without limitationpolycarbonates, polyfumarates, and caprolactones. The manifold 111 mayfurther serve as a scaffold for new cell growth, or may be used inconjunction with the scaffold 112 to promote cell-growth.

The manifold 111 may further promote granulation at the tissue site 102as reduced pressure is applied through the reduced pressure dressing110. For example, any or all of the surfaces of the manifold 111 mayhave an uneven, course, or jaded profile that causes microstrains andstresses at the scaffold 112 and the tissue site 102 when reducedpressure is applied through the manifold 111. These microstrains andstresses have been shown to increase new tissue growth.

The scaffold 112 may be placed adjacent to, in contact with, orsubstantially over the tissue site 102 to promote the growth of thecartilage in the wound 106. As indicated above, the scaffold 112 mayalso function as a manifold when transferring reduced pressure to thetissue site 102. The scaffold 112 is a three-dimensional porousstructure that provides a template for cell growth of the cartilage 108within the wound 106. Nonlimiting examples of scaffold materials includecalcium phosphate, collagen, PLA/PGA, hydroxyapatite, carbonates, andprocessed allograft materials. The scaffold 112 may also assist indelivering fluids to, or removing fluids from, the tissue site 102. Thescaffold 112 may further comprise a distribution surface 122 that ispositioned adjacent to the wound 106 to facilitate fluid flow,chondrocyte migration, and the like for moving a fluid and othermaterial to or from the tissue site 102 to the pores in the scaffold112. In some embodiments, the scaffold 112 is flexible to conform to theshape or contour of the wound 106 at the tissue site 102. The design ofthe scaffold 112 may also serve to prevent cartilage overgrowth. Theshape and flexibility of the scaffold 112 may be selected without undueexperimentation depending on the type of cartilage being treated in thelocation of the cartilage in the body treated.

A chondrocyte or chondrocyte precursor may be grafted, or otherwiseapplied, to the tissue site 102 or the scaffold 112 to facilitate thegrowth of the cartilage 108. An example of a chondrocyte precursor is amesenchymal stem cell. The source of the chondrocyte or chondrocyteprecursor may be an osteochondral graft, autologous to the patient, orcomprising allograft, xenograft, or artificially prepared tissue. In oneembodiment, the tissue source may be chondrocytic cell cultures, such aschondrocyte or stem cell cultures which have been prepared through exvivo cell culture methods, with or without additional growth factors.For examples of cell culture methods, see, e.g., U.S. Pat. Nos.5,226,914; 5,811,094; 5,053,050; 5,486,359; 5,786,217 and 5,723,331. Thetissue may also be harvested by traditional non-cell culture basedmeans, using techniques such as mosaicplasty, in which cartilage isharvested using commercially available instruments such as Acufex7, CORSystem, or Arthrex7 Osteochondral Autograft Transfer System. Further,the tissue harvested may be applied directly to the scaffold 112, or maybe cultured beforehand.

The cells, chondrocyte, or chondrocyte precursor may be transfected,either transiently or stably, to further comprise a recombinant nucleicacid. Non-limiting examples of such nucleic acids include those thatencode a protein, such as a cytokine, an enzyme, or a regulatoryprotein; a regulatory nucleic acid such as a promoter that causes anative protein to be overexpressed or silenced (e.g., to inhibit cancerinitiation or growth); an miRNA or another RNAi molecule; an antisensemolecule; a marker to assist in monitoring tissue formation; etc. Theskilled artisan can determine and prepare, without undueexperimentation, a chondrocyte or chondrocyte precursor comprising anappropriate recombinant nucleic acid for any particular application.

Other cells may also be seeded onto the scaffold 112 and/or placed on orinto the tissue site 102 to stimulate the growth of cartilage.Non-limiting examples include fibroblasts, immune cells, stem cells thatare not a chondrocyte precursor, etc. In some embodiments, attachment ofthe cells to the scaffold 112 may be enhanced by coating the scaffold112 with compounds such as basement membrane components, agar, agarose,gelatin, gum arabic, collagen types I, II, III, IV, and V, fibronectin,laminin, glycosaminoglycans, polyvinyl alcohol, mixtures thereof, andother hydrophilic and peptide attachment materials known to thoseskilled in the art of cell culture. In another embodiment, the cells areseeded onto the scaffold 112, and the scaffold 112 is incubated beforethe scaffold 112 is applied to the tissue site 102.

A cytokine may be applied to the tissue site 102 or in the scaffold 112as indicated above. As used herein, a cytokine is a protein that affectscellular growth, proliferation or differentiation, including growthfactors and hormones. In some embodiments, the cytokine is one that canencourage cartilage growth. Nonlimiting examples include bonemorphogenic protein (BMP)-2, BMP-6, BMP-7, transforming growth factor-β(TGF-β), insulin-like growth factor (IGF), platelet-derived growthfactor (PDGF), or cartilage-derived retinoic acid sensitive protein(CD-RAP). The cytokine may be synthetic or naturally produced, orproduced naturally or transgenically by cells placed at the tissue site102 or in the scaffold 112.

The scaffold 112 may include, without limitation, calcium phosphate,collagen, PLA/PGA, hydroxyapatite, carbonates, and/or processedallograft materials. In another embodiment, the scaffold 112 may be usedto release at least one therapeutic or prophylactic agent to the tissuesite 102 by binding at least one therapeutic or prophylactic agent tothe surface of the scaffold 112. For example, an antibiotic may also beapplied to the scaffold 112, which is then released to the tissue site102.

In some embodiments, the scaffold 112 is a porous material that includesa plurality of open chambers or “pores” that are connected by flowchannels to allow fluid communication between the pores. The size,shape, or interconnectivity of the pores may be uniform, random, orpatterned, and may be altered to enhance or control cartilage formation,response, repair, or host integration. Further, the size, shape, orinterconnectivity of the pores in the scaffold 112 may be altered toenhance or control the integration of newly formed cartilage 108 withsurrounding healthy tissue at the tissue site 102. In variousembodiments, the scaffold 112 has a high void-fraction (i.e., a highcontent of air). It is desired in some embodiments that the pores aredesigned to allow the attachment of infiltrating cells to induce newcartilage formation. As explained above, the pores and flow chambers maybe seeded with chondrocytes or other cell types in advance to promotecartilage formation. The flow channels in the scaffold 112 alsofacilitate distribution of fluids provided to and removed from thetissue site 102, including the transfer of reduced pressure to thetissue site 102.

In one embodiment, the scaffold 112 is made primarily of an open porematerial that includes a plurality of pores fluidly connected toadjacent pores, where a plurality of flow channels is formed by andbetween the open pores of the material. The variations in size and shapeof the pores results in variations in flow channels and can be used toalter flow characteristics of fluid through the material. In someembodiments, the scaffold 112 pore size ranges between 25 μm and 500 μm.In other embodiments, the pore size is between 50 μm and 250 μm. Inadditional embodiments, the pore size is between 50 μm and 150 μm.

The scaffold 112 may be formed of any biocompatible material, i.e. amaterial that does not elicit any undesirable local or systemic effectsin vivo. A biocompatible scaffold 112 should also have the mechanicaland biochemical properties that provide adequate support for tissuegrowth and cell proliferation. The materials can be characterized withrespect to mechanical properties such as tensile strength using anInstron tester, molecular weight by gel permeation chromatography (GPC),glass transition temperature by differential scanning calorimetry (DSC)and bond structure by infrared (IR) spectroscopy. The material may alsobe characterized with respect to toxicology by, for example, mutagentests, e.g. involving an Ames assay or an in vitro teratogenicity assay,or biochemical, cell, or implantation studies in animals forimmunogenicity, inflammation, release or degradation.

In one embodiment, the scaffold 112 is formed of a bio-inert material,i.e., a material that does not elicit any response in vivo and does notbioabsorb or otherwise degrade in vivo. In another embodiment, thescaffold 112 is formed of a bioabsorbable material as that term indefined above. Regardless of whether the scaffold 112 is bioabsorbableor bio-inert when it contacts the tissue site 102, the scaffold 112 mayalso be biocompatible. If the scaffold 112 is made of bioabsorbablematerials, the materials may be designed to degrade within a desiredtime frame. In one embodiment, the desired degradation time frame is sixto twelve weeks. In another embodiment, the desired degradation timeframe is between three months and one year. In yet another embodiment,the desired degradation time is greater than a year. Further, in someembodiments, scaffolds 112 made of bioabsorbable materials may degradein a manner related to the molecular weights of the materials used tomake the scaffold 112. In those embodiments, scaffolds 112 comprising ahigher molecular weight material often retain structural integrity forlonger periods of time than scaffolds 112 comprising lower molecularweight materials.

The scaffold 112 may be formed by melt-spinning, extrusion, casting, orother techniques well known in the polymer processing area. Preferredsolvents, if used, are those which are removed by the processing orwhich are biocompatible in the amounts remaining after processing.Examples of polymers which can be used to form scaffolds 112 includenatural and synthetic polymers. Synthetic polymers that may be usedinclude, but are not limited to, bioabsorbable polymers such aspolylactic acid (PLA), polyglycolic acid (PGA), polylactic-coglycolideacid (PLGA), and other polyhydroxyacids, polycaprolactones,polycarbonates, polyamides, polyanhydrides, polyamino acids, polyorthoesters, polyacetals, degradable polycyanoacrylates and degradablepolyurethanes, as well as a polylactide-coglycolide (PLAGA) polymer or apolyethylene glycol-PLAGA copolymer. Examples of natural polymersinclude, but are not limited to, proteins such as albumin, collagen,fibrin, and synthetic polyamino acids, and polysaccharides such asalginate, heparin, and other naturally occurring biodegradable polymersof sugar units. The polymeric blend may also include without limitationpolycarbonates, polyfumarates, and capralactones.

In some embodiments, the bioabsorbable scaffold 112 is made of PLA, PGAor PLA/PGA copolymers. PLA polymers may be prepared from the cyclicesters of lactic acids. Both L (+) and D (−) forms of lactic acid can beused to prepare the PLA polymers, as well as the optically inactiveDL-lactic acid mixture of D (−) and L (+) lactic acids. PGA is thehomopolymer of glycolic acid (hydroxyacetic acid). Typically, in theconversion of glycolic acid to polyglycolic acid, glycolic acid isinitially reacted with itself to form the cyclic ester glycolide, whichin the presence of heat and a catalyst is converted to a high molecularweight linear-chain polymer. It is also contemplated that the scaffold112 may be felted mats, liquids, gels, foams, or any other biocompatiblematerial that provides fluid communication through a plurality ofchannels in three dimensions.

The drape 114 covers the reduced pressure dressing 110 and serves as asemi-permeable barrier to transmission of fluids such as liquids, air,and other gases. The drape 114, which in some embodiments providesstructural support for the reduced pressure dressing 110, may be coupledto the reduced pressure dressing 110 or the manifold 111 using anytechnique, including via an adhesive. As used herein, the term “coupled”includes coupling via a separate object and includes direct coupling.The term “coupled” also encompasses two or more components that arecontinuous with one another by virtue of each of the components beingformed from the same piece of material. Also, the term “coupled” mayinclude chemical, such as via a chemical bond, mechanical, thermal, orelectrical coupling. Specific non-limiting examples of the techniques bywhich the manifold 111 may be coupled to the drape 114 include welding(e.g., ultrasonic or RF welding), bonding, adhesives, cements, etc. Inalternative embodiments, the drape 114 is not a separate, attachedstructure, but instead the manifold 111 itself may include a lining ofimpermeable materials that functions the same as the drape 114.

The drape may be any material that provides a pneumatic or fluid seal.The drape may, for example, be an impermeable or semi-permeableelastomeric material. “Elastomeric” means having the properties of anelastomer. It generally refers to a polymeric material that hasrubber-like properties. More specifically, most elastomers haveelongation rates greater than 100% and a significant amount ofresilience. The resilience of a material refers to the material'sability to recover from an elastic deformation. Nonlimiting examples ofelastomers include natural rubbers, polyisoprene, styrene butadienerubber, chloroprene rubber, polybutadiene, nitrile rubber, butyl rubber,ethylene propylene rubber, ethylene propylene diene monomer,chlorosulfonated polyethylene, polysulfide rubber, polyurethane, EVAfilm, co-polyester, and silicones. Specific examples of drape materialsinclude a silicone drape, 3M Tegaderm® drape, acrylic drape such as oneavailable from Avery Dennison, or an incise drape.

In operation, the system 100 is used to stimulate formation of cartilageat the tissue site 102. A caretaker can apply a chondrocyte orchondrocyte precursor to the tissue site 102 or the reduced pressuredressing 110, and then apply reduced pressure to the tissue site 102 viathe manifold 111 and the scaffold 112 for a time sufficient to cause newcartilage formation at the tissue site 102. The application of reducedpressure can result in the flexible drape 114 compressing and conformingto the surface of the tissue site 102 as air is removed from within thespace between the drape 114 and the tissue site 102. In someapplications, the system 100 may be used to cosmetically alter tissuehaving cartilage, such as a nose or ear. Cartilage may also be harvestedon one mammal and then transplanted to another mammal, e.g., growing anose or ear on a mouse for transplantation to a human. The system 100may also be applied to a cartilage wound 106 and used to at leastpartially fill the wound 106.

The system 100 may also allow effective control of fixation,temperature, pressure (and its associated gradients for vital gases suchas oxygen), osmotic forces, oncotic forces, and the addition or removalof various nutrients and pharmacological agents. Still further, thedevices to apply reduced pressure in the current system and methodologymay be enabled to transfer elements for the manipulation of gas andliquid pathways by preprogrammed, coordinated influx and efflux cycles.Such cycles would be designed to maintain the desired integrity andstability of the system while still allowing variations in multipleforces, flows, and concentrations within tolerated ranges.

The system 100 may also be configured to deliver fluid, liquids or gas,to the tissue site 102. In this embodiment, a fluid supply 124 fordelivering a fluid 125 to the tissue site 102 fluidly communicates withthe reduced pressure dressing 110 by a conduit 126 that may be connecteddirectly to the reduced pressure dressing 110 (not shown) or indirectlyvia the conduit 118 which requires the use of valves 127 and 128 forcontrolling the delivery of reduced pressure from the reduced pressuresource 116 and/or fluid 125 from the fluid supply 124, respectively. Thefluid supply 124 may be separate from, attached to, or integrated withinthe reduced-pressure source 116. The fluid supply 124 enables treatmentprocedures to infuse the tissue site 102 with fluids to flushcontaminants, counter infection, or promote tissue growth in the wound106. Thus, the fluid supply 124 can be used to deliver variousirrigation fluids, growth factors, antibiotics, anesthetics,antibacterial agents, antiviral agents, cell-growth promotion agents, orchemically active agents to the tissue site 102. The fluid supply 124can also be used to deliver gaseous fluids to the tissue site 102 for asimilar purpose including, for example, the delivery of sterile air insmall quantities to promote and maintain the therapeutic effect at thetissue site 102 with or without the reduced pressure being maintained.

Referring to FIG. 2, a flow chart is provided outlining an illustrativeembodiment of a method of administering reduced-pressure therapy to atissue site requiring cartilage regeneration or healing by use of thereduced pressure system. First, the tissue area of interest isidentified, for example, by a caretaker (step 201). If the tissue siteis located underneath the skin of a patient, i.e., not in direct line ofsight, the caretaker may identify the tissue site by use of imagingequipment and techniques, such as MRI imaging. At this time, thecaretaker would then determine the best path through the patient's bodyto reach the tissue area which would cause the least damage to healthy,normal tissues.

The manifold is then delivered to the tissue site (step 202). Further,depending upon the embodiment, conduits to deliver reduced pressure,fluids, gases, or air may be connected before or after the manifold isdelivered to the tissue site. If the tissue site is located underneaththe skin of the patient, the manifold may be delivered to the tissuesite by insertion into the body through the skin of the patient andthrough any interstitial tissue.

In some embodiments, it is contemplated that the tissue site hasinsufficient space to insert a manifold. In these embodiments, a devicemay be inserted that creates a void. For example, this device may be aninflatable device. Once a void is prepared, the manifold may then bedelivered.

The main distribution surface of the manifold is then positionedadjacent to the tissue site (step 203). A reduced pressure is thenapplied to the tissue site (step 204). The reduced pressure may beapplied continuously or in an intermittent fashion. Further, it iscontemplated that the reduced pressure may be alternated with deliveryof fluids, air, or agents that promote healing or regeneration aspreviously discussed.

The length and force of the reduced-pressure therapy may depend uponvarious factors determined appropriate by a caretaker, such as previousexperience, connective tissue regeneration rate, and the like. Themanifold may be removed upon partial or complete regeneration of thecartilage (step 205).

In some embodiments, the open pores or flow channels of the scaffold maybe designed to promote a certain connective tissue growth in aparticular three-dimensional shape. Thus, in one embodiment, thescaffold may be designed to promote cartilage growth on the surface ofthe body such as, for example, an ear. Referring more specifically toFIG. 3, an illustrative embodiment of a system 300 for applyingreduced-pressure therapy to an ear 301 at a tissue site 302 on the topof the ear 301 is shown. This illustrative embodiment of the system 300applies reduced-pressure therapy to a missing section of the ear 301, orcartilage wound 306, to regenerate the missing cartilage. The cartilagewound 306 of the tissue site 302 may have been due to any causeincluding, for example, trauma, surgery, or cancer. The system 300comprises a reduced pressure dressing 303 which includes a manifold 311adapted to distribute the reduced pressure to the tissue site 302 and ascaffold 312 adapted for placement adjacent the cartilage wound 306, anda drape 314 at least partially covering the reduced pressure dressing303 to provide an airtight seal covering the cartilage wound 306 at thetissue site 302. The remaining components of the system 300 include thesame components comprising the system 100 described above including, forexample, the tube adapter 120 fluidly coupling the conduit 118 to thereduced pressure dressing 303. All the components of the system 300described above operate in a fashion similar to the components of thesystem 100.

As indicated above, the scaffold 312 may be placed adjacent to, incontact with, or substantially over the tissue site 302 to promote thegrowth of the cartilage in the cartilage wound 306. The scaffold 312 isa three-dimensional porous structure that provides a template for cellgrowth of the cartilage within the wound 306. The shape and flexibilityof the scaffold 312 may be selected based on the desired shape of theear 301 as indicated by the dashed line on the reduced pressure dressing303. In one embodiment, a mold (not shown) may be used to form thescaffold 312 into the desired shape. Once the mold is created to fit theear 301 at the tissue site 302 with the missing portion, it can be usedto form the scaffold 312 into the three-dimensional shape desired torepair the cartilage wound 306. As indicated above, the scaffold 312 maycontain chondrocytes or a coping may be applied directly to thecartilage wound 306. When the reduced pressure dressing 303 includingthe scaffold 312 is positioned within the void of the cartilage wound306, the drape 314 is positioned to cover the reduced pressure dressing303 as described in detail above. Reduced pressure therapy can then beapplied by use of the reduced-pressure source (not shown) via theconduits 118 fluidly coupled to the reduced pressure dressing 303.

In another embodiment, the mold may be positioned over the cartilagewound 306 creating a void that may be filled with a fluid containingchondrocytes that is delivered by a fluid supply (not shown) via theconduit 118 or other independent supply of fluid. After the fluid fillsthe void between the mold and the cartilage wound 306, the fluid hardensto form the three-dimensional scaffold 312 that assumes the desiredshape for the regenerated cartilage at the tissue site 302. The scaffoldmay also be seeded with chondrocytes after hardening.

Other embodiments within the scope of the claims herein will be apparentto one skilled in the art from consideration of the specification orpractice of the invention as disclosed herein. It is intended that thespecification, together with the examples, be considered exemplary only,with the scope and spirit of the invention being indicated by theclaims, which follow the example. An illustrative embodiment isdescribed in the following example.

Example Induction of Cartilage Tissue Formation

Cartilage formation was observed in response to the application ofreduced pressure therapy to the surface of intact cranial periostealmembranes. These observations are of significance in that cartilageformation in response to a therapy is unique and of great interest inthe field of tissue engineering. These formations were observed in theabsence of scaffold materials and only with the application of reducedpressure. No cartilage formation was observed in controls not subjectedto reduced pressure.

Cartilage degeneration caused by congenital abnormalities or disease andtrauma is of great clinical consequence. Because of the lack of bloodsupply and subsequent wound-healing response, damage to cartilagegenerally results in an incomplete repair by the body. Full-thicknessarticular cartilage damage, or osteochondral lesions, allow for thenormal inflammatory response, but result in inferior fibrocartilageformation. Surgical intervention is often the only option. Treatmentsfor repair of cartilage damage are often less than satisfactory, andrarely restore full function or return the tissue to its native normalstate. This Example demonstrates the induction of new cartilage fromperiosteum using GranuFoam® and reduced pressure treatment.

A foam manifold and reduced pressure were evaluated for their ability toinduce the periosteum to synthesize new cartilage. The intact, undamagedcrania of rabbits were exposed. A GranuFoam® (KCI Licensing, Inc., SanAntonio Tex.) foam dressing was applied to the bone. With sometreatments, the foam-covered bone was also subjected to reducedpressure. After treatment, the treated bone was subjected to paraffinembedding, sectioning, and staining to evaluate the effect of thetreatment on new bone formation.

FIG. 4A shows a naïve, undamaged periosteum in rabbit cranium. The dotsdenote the demarcation between the cortical bone and the thin layer ofthe periosteum. By contrast, FIGS. 4B and 4C show that, with the use ofGranuFoam® and reduced pressure (−125 mm Hg), extensive cartilagetissues was induced overlying the periosteum.

In view of the above, it will be seen that the several advantages of theinvention are achieved and other advantages attained. As various changescould be made in the above methods and compositions without departingfrom the scope of the invention, it is intended that all mattercontained in the above description and shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

All references cited in this specification are hereby incorporated byreference. The discussion of the references herein is intended merely tosummarize the assertions made by the authors and no admission is madethat any reference constitutes prior art. Applicants reserve the rightto challenge the accuracy and pertinence of the cited references.

1. A method of inducing new cartilage growth from periosteum in amammal, the method comprising: positioning a foam manifold in contactwith the periosteum; positioning a drape over the foam manifold and theperiosteum to create a sealed space between the drape and theperiosteum; applying a reduced pressure to the sealed space.
 2. Themethod of claim 1, wherein the new cartilage growth-overlies theperiosteum.
 3. The method of claim 1, wherein the periosteum is intactand undamaged.
 4. The method of claim 1, wherein the reduced pressure isapplied to the sealed space by a reduced pressure source.
 5. The methodof claim 1 further comprising applying a chondrocyte or chondrocyteprecursor to the periosteum.
 6. The method of claim 5, wherein thechondrocyte or chondrocyte precursor is a mesenchymal stem cell.
 7. Themethod of claim 1, wherein the foam manifold is a biocompatiblescaffold.
 8. The method of claim 7, wherein the biocompatible scaffoldcomprises a polyhydroxy acid, a poly(caprolactone), a polycarbonate, apolyamide, a polyanhydride, a polyamino acid, a polyortho ester, apolyacetal, a degradable polycyanoacrylate or a degradable polyurethane.9. The method of claim 7, wherein the biocompatible scaffold comprises apolylactide-coglycolide (PLAGA) polymer or a polyethylene glycol-PLAGAcopolymer.
 10. The method of claim 1, wherein the foam manifold is abioabsorbable scaffold.
 11. A method of stimulating cartilage formationat a tissue site having periosteum, the method comprising: applying afoam manifold to the periosteum; and applying reduced pressure to thefoam manifold and the tissue site for a time sufficient to cause newcartilage formation at the tissue site.
 12. The method of claim 11,wherein the new cartilage overlies the periosteum.
 13. The method ofclaim 11, wherein the periosteum is intact and undamaged.
 14. The methodof claim 11, wherein the reduced pressure is applied to the foammanifold and the tissue site by a reduced pressure source.
 15. Themethod of claim 11 further comprising applying a chondrocyte orchondrocyte precursor to the periosteum.
 16. The method of claim 15,wherein the chondrocyte or chondrocyte precursor is a mesenchymal stemcell.
 17. The method of claim 11, wherein the foam manifold is abiocompatible scaffold.
 18. The method of claim 17, wherein thebiocompatible scaffold comprises a polyhydroxy acid, apoly(caprolactone), a polycarbonate, a polyamide, a polyanhydride, apolyamino acid, a polyortho ester, a polyacetal, a degradablepolycyanoacrylate or a degradable polyurethane.
 19. The method of claim17, wherein the biocompatible scaffold comprises apolylactide-coglycolide (PLAGA) polymer or a polyethylene glycol-PLAGAcopolymer.
 20. The method of claim 11, wherein the foam manifold is abioabsorbable scaffold.
 21. A system for stimulating cartilage formationat a tissue site comprising: a foam manifold positioned in contact withperiosteum at the tissue site; a drape positioned over the foam manifoldand the tissue site to create a sealed space between the drape and thetissue site; a reduced pressure source in fluid communication with thesealed space.
 22. The method of claim 21, wherein new cartilage growthis stimulated by the reduced pressure applied to the sealed space, andthe new cartilage overlies the periosteum.
 23. The method of claim 21,wherein the periosteum is intact and undamaged.
 24. The method of claim21 further comprising a chondrocyte or chondrocyte precursor in contactwith the foam manifold or the periosteum.
 25. The method of claim 24,wherein the chondrocyte or chondrocyte precursor is a mesenchymal stemcell.
 26. The method of claim 21, wherein the foam manifold is abiocompatible scaffold.
 27. The method of claim 26, wherein thebiocompatible scaffold comprises a polyhydroxy acid, apoly(caprolactone), a polycarbonate, a polyamide, a polyanhydride, apolyamino acid, a polyortho ester, a polyacetal, a degradablepolycyanoacrylate or a degradable polyurethane.
 28. The method of claim26, wherein the biocompatible scaffold comprises apolylactide-coglycolide (PLAGA) polymer or a polyethylene glycol-PLAGAcopolymer.
 29. The method of claim 21, wherein the foam manifold is abioabsorbable scaffold.